A known hypocycloid reduction gear device includes an internal gear (ring gear) having internal teeth formed on the inner periphery thereof, an external gear (planetary gear) having external teeth on the outer periphery thereof meshing with the internal teeth and an eccentric drive member rotatably supported by a fixed member in a coaxial relationship to the internal gear and rotatably supporting the external gear such that the external gear rolls over the inner periphery of the internal gear while maintaining the meshing between the internal teeth and the external teeth. The external gear has a fewer number of gear teeth than the internal gear. See JP2007-24072A, for instance. When the external gear has gear teeth that are only one less than the internal gear, a maximum reduction ratio can be achieved.
In such a hypocycloid reduction gear device, because the external gear is caused to wobble while rolling over the inner periphery of the internal gear owing to the action of the eccentric drive member, a certain coupling is required between the external gear and the fixed member in order to accommodate the wobbling motion of the external gear while the external gear and the fixed member are kept rotationally fast to each other. Therefore, a relatively complex shaft coupling such as an Oldham coupling is required for this purpose in order to minimize wears and noises. In the prior art disclosed in JP2007-24072A, in order to accommodate the wobbling motion of the external gear, a plurality of roller pins extending axially from a fixed member are received in respective circular holes provided in the external gear.
In particular, for use as the reduction gear devices in the actuators of robots, the known devices are considered to be inadequate in terms of durability, noise level and compactness.
In view of such problems of the prior art, a primary object of the present invention is to provide a wobble removal shaft coupling that is highly durable, capable of quiet operation and highly compact.
A second object of the present invention is to provide a hypocycloid reduction gear device incorporated with such a wobble removal shaft coupling.
The present invention accomplishes such an object by providing a wobble removal shaft coupling, comprising: a wobble removal gear (52) comprising an internal gear having a set of internal gear teeth (60) along an inner circumference thereof, and having a first central axial line; and an external gear (18) meshing with the wobble removal gear via a set of external gear teeth (16) and having a second central axial line, the first and second central axial lines being in parallel with and offset from each other, and the external gear teeth (16) being identical in number to the internal gear teeth (60) of the wobble removal gear; wherein at least one of the two sets of the gear teeth are resiliently deformable in a circumferential and/or radial direction.
The resiliently deformable gear teeth cause the external gear to be rotationally fast with the wobble removal gear (although the external gear rolls over the inner periphery of the wobble removal gear) while permitting the wobbling motion of the external gear relative to the wobble removal gear without involving a play or a sliding engagement.
The resiliently deformable set of gear teeth (60) may be formed by laminating a plurality of laminates (53) so that the manufacturing cost can be minimized and the manufacturing process can be simplified.
To enhance the resiliency or compliance of the resiliently deformable gear teeth, the resiliently deformable gear teeth (60) may be separated from one another by a radial slit (56) having a greater length than an effective height of the resiliently deformable gear teeth.
To even further enhance the resiliency or compliance of the resiliently deformable gear teeth, each of the resiliently deformable gear teeth may be provided with a central radial slot (63, 65) extending radially in a base end portion thereof.
The central radial slot (65) may extend through a free end portion of the corresponding resiliently deformable gear tooth (60) such that the resiliently deformable gear tooth is formed as a bifurcated tooth.
According to a preferred embodiment of the present invention, the gear provided with the resiliently deformable set of gear teeth (60) is provided with a plurality of mounting pieces (62) each formed by partly omitting the slits and truncating the corresponding gear teeth and having a mounting hole (57) formed therein. Thereby, the mounting hole may be formed without unduly increasing the diameter of the corresponding gear. The omission of the slits and the truncation of the affected gear teeth should be performed such that a proper meshing between the wobble removal gear and the external gear can be maintained.
To enhance the resiliency or compliance of the resiliently deformable gear teeth while optimizing the stress distribution in each resiliently deformable gear tooth, the resiliently deformable gear tooth (60) may be provided with a free end portion configured as an effective gear tooth and a base portion which is substantially narrower than the free end portion.
According to another embodiment of the present invention, each resiliently deformable gear tooth (60) includes a curved support piece extending between an effective gear tooth and a gear main body so that the resiliency or compliance of the resiliently deformable gear teeth can be enhanced. For instance, each curved support piece may meander in the radial direction as it extends radially.
To positively define the limit of the range of deformation of each resiliently deformable gear tooth, the gear tooth (60) may be provided with a circumferential extension (67) opposing an adjacent gear tooth or a similar circumferential extension at a small gap.
The present invention also provides a wobble removal shaft coupling (70) comprising: an inner wheel (72); an outer wheel (74) disposed substantially concentric to the inner wheel (72); and a resilient member (76) connecting the inner wheel (72) and the outer wheel (74) to each other so as to be resiliently moveable in a circumferential and/or radial direction relative to each other; wherein the resilient member (76, 100, 102, 130) includes a support piece extending between the inner wheel and the outer wheel in a circumferentially meandering fashion or in a spirally curved fashion.
To positively define the limit of the range of deformation of each resiliently deformable gear tooth, the inner wheel (72) and the outer wheel (74) may be provided with abutting portions (82, 88) that limit relative movement between the inner wheel and the outer wheel beyond a prescribed limit.
The inner wheel, the outer wheel and the resilient member may be formed by laminating a plurality of laminates (53) each integrally provided with parts corresponding to the inner wheel, the outer wheel and the resilient member so that the manufacturing cost can be minimized and the manufacturing process can be simplified.
The present invention also provides a hypocycloid reduction gear device comprising: a base member (40); an internal gear (14) having internal gear teeth (12) along an inner circumference thereof, and supported by the base member so as to be rotatable around a first rotational center line; an external gear (18) having external gear teeth (16) along an outer circumference thereof, the external gear teeth meshing with the internal gear teeth, and the external gear teeth being smaller in number than the internal gear teeth; an eccentric drive member (24) rotatably supported by the base member so as to be rotatable around the first rotational center line, and rotatably supporting the external gear so as to be rotatable around a second rotational center line extending in parallel with and offset from the first rotational center line and roll over the inner circumference of the internal gear; and a wobble removal shaft coupling (50, 70) for resiliently coupling the external gear with the base member so as to maintain the external gear rotatively fixed relative to the base member while permitting an eccentric wobbling movement of the external gear relative to the base member.
In a typical application, the base member may consist of a fixed member.
The resiliently deformable gear teeth cause the external gear to be rotationally fast with the wobble removal gear (although the external gear rolls over the inner periphery of the wobble removal gear) while permitting the wobbling motion of the external gear relative to the wobble removal gear without involving a play or a sliding engagement. Furthermore, the meshing between the external gear teeth and the internal gear teeth can achieve a high speed reduction ratio.
According to a certain aspect of the present invention, the wobble removal shaft coupling (50) comprises a wobble removal gear (52) having a set of wobble removal internal gear teeth (60) along an inner circumference thereof and fixedly attached to the base member in a substantially concentric relationship to the internal gear (14), the wobble removal internal gear teeth (60) meshing with the set of the external gear teeth (16), and the external gear teeth being identical in number to the wobble removal internal gear teeth of the wobble removal gear; wherein at least one of the two sets of the gear teeth are resiliently deformable in a circumferential and/or radial direction.
According to another aspect of the present invention, the wobble removal shaft coupling (70) comprises: an inner wheel (72) fixedly attached to the external gear (18); an outer wheel (74) disposed substantially concentric to the inner wheel and fixedly attached to the base member; and a resilient member (76, 100, 102, 130) connecting the inner wheel and the outer wheel to each other so as to be resiliently moveable in a circumferential and/or radial direction relative to each other; wherein the resilient member includes a support piece extending between the inner wheel and the outer wheel in a circumferentially meandering fashion or in a spirally curved fashion.